(1) Field of the Invention
The present invention relates generally to sewing machines and, more particularly, to a new and improved sewing machine for forming a faster, stronger stitch.
(2) Description of the Prior Art
The need for increasing the flow through or throughput speed, seam strength and overall general appearance for sewing operations is well established. Currently, the sewing industry uses parallel chain stitches to join two edges of apparel, such as workwear, which requires increased strength. Parallel chain stitches are typically found in such things as pant legs and shirt seams.
Although parallel chain stitches improve the strength of the edge, the flow through or throughput speed of fabric is no faster than that during the formation of conventional single chain stitch because the sewing machine usually forms the same number of stitches in order to have sufficient seam strength. Moreover, while seams of parallel chain stitches are stronger than seams of a single chain stitch, there is a need for even stronger seams that would hold up under even harsher conditions. Parallel chain stitches are formed primarily to have the redundancy of backing one another up but do not actually reinforce the strength of one another.
FIG. 1A shows a schematic of a needle represented by a dot of a single needle looking down on the flow through or throughput direction of the fabric and a reference line at about a 45 degree angle relative to the flow through or throughput direction of the fabric. The flow through or throughput direction of the fabric is designated by the arrow having its head pointing toward the top of the page. This single needle chuck arrangement produces a single chain stitch in a fabric as it is moved in the flow through or throughput direction past the single needle and the needle moves a thread in and out of the fabric.
FIG. 1B shows a schematic of two non-optional needles, each represented by a dot, and an optional needle, represent by the circled dot, of a staggered offset chuck for a flatbed-type machine looking down on the flow through or throughput direction of the fabric and a reference line at about a 45 degree angle relative to the flow through or throughput direction of the fabric. The two non-optional needles and the optional needle are aligned on the reference line. The flow through or throughput direction of fabric is designated by the arrow having its head pointing toward the top of the page. The optional needle is also the middle needle. This staggered offset chuck arrangement for a flatbedtype machine produces a parallel two chain stitch such as a riser or lap seam in fabric as it is moved in the flow through or throughput direction past each non-optional needle and the needles move separate threads in and out of the fabric. When the optional needle is included, this staggered offset chuck arrangement produces a parallel three chain stitch in fabric as it is moved in the flow through or throughput direction past each needle and the needles move separate threads in and out of the fabric. The needles are staggered or offset to create parallel chain stitches that are redundant and aligned to have substantially no stagger or offset.
FIG. 1C shows a schematic of two non-optional needles, each represented by a dot, and an optional needle, represent by the circled dot, of a staggered offset chuck for a feed-off-the-arm type machine looking down on the flow through or throughput direction of the fabric and a reference line at about a 45 degree angle relative to the flow through or throughput direction of the fabric. Only one of the non-optional needles is aligned on the reference line. The other non-optional needle and the optional needle are both off the reference line. The flow through or throughput direction of fabric is designated by the arrow having its head pointing toward the top of the page. The optional needle is also the middle needle. This staggered offset chuck arrangement for a feed-off-the-arm machine produces a parallel two chain stitch such as a fell seam or lap seam in fabric, as it is moved in the flow through or throughput direction past each non-optional needle and the needles move separate threads in and out of the fabric. When the optional needle is included, this staggered offset chuck arrangement produces a parallel three chain stitch in fabric as it is moved in the flow through or throughput direction past each needle and the needles move separate threads in and out of the fabric.
In both the flatbed-type machine and the feed-off-the-arm machine, the needles are staggered or offset to create parallel chain stitches that are redundant and aligned to have substantially no stagger or offset. The spacing of the parallel chains is dictated by the seam width and the interaction of damaged zones created within a fabric when a needle penetrated the fabric. That is, the non-optional needles must be spaced to create two parallel chain stitches that are spaced to capture the ends and end enveloping folds of the fabrics brought together by a seam, while preventing the creation of hanging or loose fabric that may catch or snag. Since the spacing of these redundant chains can be significant, each chain of the parallel two chain stitch may provide little reinforcement for the other. The non-optional needles and the optional needle must be spaced to create three parallel chain stitches that are spaced so that the damaged zones within the fabrics being brought together by the seam do not interact. Here too, each of these redundant chains of the parallel three chain stitch may provide little reinforcement for any of the other. Also as noted, since the parallel chain stitches are redundant and aligned to have substantially no stagger or offset, the flow through or throughput speed of fabric during their manufacture is no faster than that during the manufacture of a conventional single chain stitch, because the same number of stitches as a single chain stitch are formed to have sufficient seam strength. Thus, the flow through or throughput speed of fabric for the manufacture of single chain and parallel chains stitches is constrained by the mechanical limits of rotating and reciprocating parts of a machine.
Thus, there remains a need for a new and improved sewing machine and the stitch it forms, which uses a longer stitch to increase flow through or throughput speed of fabric and productivity, while at the same time, increases the pull strength of the sewn article.
The present invention is directed to a tandem sewing machine and the stitch it forms. The sewing machine includes a stand frame, a drive motor, a throatplate, and at least two offset needles. The offset needles have a needle stagger ("sgr") which, in combination with the needle spacing (D) produces a stitch stagger to displacement ratio (S/D) of greater than about 1 of the improved stitch. The resulting parallel stitching is characterized by a stitch offset or stitch stagger (S) and parallel or stitch spacing (D). It should be understood that the needle offset stagger ("sgr") is not necessarily the same as the stitch stagger (S). However, the needle spacing (D) is substantially equal to the parallel stitch spacing (D). The sewing machine may also includes an overedge stitching needle assembly and a compound feed assembly.
In the preferred embodiment, the compound feed assembly includes a bottom feed dog and a top feed dog, wherein the top feed dog is a differential feed with respect to the bottom feed dog. The sewing machine may further include a second bottom feed dog, which may also be a differential feed. In the preferred embodiment, the overedge stitching needle assembly includes at least one needle performing an overedge stitch.
It has been discovered that where the S/D ratio is greater than or equal to about 1, there is a substantial increase in pull strength which allows the stitch length to be greatly lengthened, thereby substantially increasing flow through or throughput speed of fabric and productivity. In the preferred embodiment, the S/D ratio is greater than about 1.3 and, preferably, about 20.
Accordingly, one aspect of the present invention is to provide a tandem sewing machine. The sewing machine includes a stand frame, a drive motor, a throatplate, and least two offset needles, wherein stitch formed by the offset needles has a stagger to displacement ratio (S/D) of greater than about 1.
Another aspect of the present invention is to provide a tandem sewing machine. The sewing machine includes a stand frame, a drive motor, a throatplate, and at least two offset needles, wherein the stitch formed by the offset needles has a stagger to displacement ratio (S/D) of greater than about 1, and an overedge stitching needle assembly.
Still another aspect of the present invention is to provide a tandem sewing machine. The sewing machine includes a stand frame; a drive motor; a throatplate; and at least two offset needles wherein stitch formed by the offset needles has a stagger to displacement ratio (S/D) of greater than about 1; an overedge stitching needle assembly; and a compound feed assembly.
The present invention is also directed to an improved stitch. The improved stitch is a parallel, offset chain stitch having a stagger to displacement ratio (S/D) of greater than about 1. It has been discovered that where the S/D ratio is greater than or equal to about 1, there is a substantial increase in pull strength, which allows the stitch length to be greatly lengthened. Also, it has been discovered that where the stitches are greatly lengthened, there is a substantial increase in fabric flow through or throughput speed, thereby substantially increasing productivity. In the preferred embodiment, the S/D ration is greater than about 1.3 and, preferably, about 20.
Accordingly, one aspect of the present invention is the stitch having a S/D ratio greater than or equal to about 1 and an overedge stitch.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.